LXR linux/block/blk-softirq.c

   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * Functions related to softirq rq completions
   4 */
   5#include <linux/kernel.h>
   6#include <linux/module.h>
   7#include <linux/init.h>
   8#include <linux/bio.h>
   9#include <linux/blkdev.h>
  10#include <linux/interrupt.h>
  11#include <linux/cpu.h>
  12#include <linux/sched.h>
  13#include <linux/sched/topology.h>
  14
  15#include "blk.h"
  16
  17static DEFINE_PER_CPU(struct list_head, blk_cpu_done);
  18
  19/*
  20 * Softirq action handler - move entries to local list and loop over them
  21 * while passing them to the queue registered handler.
  22 */
  23static __latent_entropy void blk_done_softirq(struct softirq_action *h)
  24{
  25        struct list_head *cpu_list, local_list;
  26
  27        local_irq_disable();
  28        cpu_list = this_cpu_ptr(&blk_cpu_done);
  29        list_replace_init(cpu_list, &local_list);
  30        local_irq_enable();
  31
  32        while (!list_empty(&local_list)) {
  33                struct request *rq;
  34
  35                rq = list_entry(local_list.next, struct request, ipi_list);
  36                list_del_init(&rq->ipi_list);
  37                rq->q->softirq_done_fn(rq);
  38        }
  39}
  40
  41#ifdef CONFIG_SMP
  42static void trigger_softirq(void *data)
  43{
  44        struct request *rq = data;
  45        unsigned long flags;
  46        struct list_head *list;
  47
  48        local_irq_save(flags);
  49        list = this_cpu_ptr(&blk_cpu_done);
  50        list_add_tail(&rq->ipi_list, list);
  51
  52        if (list->next == &rq->ipi_list)
  53                raise_softirq_irqoff(BLOCK_SOFTIRQ);
  54
  55        local_irq_restore(flags);
  56}
  57
  58/*
  59 * Setup and invoke a run of 'trigger_softirq' on the given cpu.
  60 */
  61static int raise_blk_irq(int cpu, struct request *rq)
  62{
  63        if (cpu_online(cpu)) {
  64                call_single_data_t *data = &rq->csd;
  65
  66                data->func = trigger_softirq;
  67                data->info = rq;
  68                data->flags = 0;
  69
  70                smp_call_function_single_async(cpu, data);
  71                return 0;
  72        }
  73
  74        return 1;
  75}
  76#else /* CONFIG_SMP */
  77static int raise_blk_irq(int cpu, struct request *rq)
  78{
  79        return 1;
  80}
  81#endif
  82
  83static int blk_softirq_cpu_dead(unsigned int cpu)
  84{
  85        /*
  86         * If a CPU goes away, splice its entries to the current CPU
  87         * and trigger a run of the softirq
  88         */
  89        local_irq_disable();
  90        list_splice_init(&per_cpu(blk_cpu_done, cpu),
  91                         this_cpu_ptr(&blk_cpu_done));
  92        raise_softirq_irqoff(BLOCK_SOFTIRQ);
  93        local_irq_enable();
  94
  95        return 0;
  96}
  97
  98void __blk_complete_request(struct request *req)
  99{
 100        int ccpu, cpu;
 101        struct request_queue *q = req->q;
 102        unsigned long flags;
 103        bool shared = false;
 104
 105        BUG_ON(!q->softirq_done_fn);
 106
 107        local_irq_save(flags);
 108        cpu = smp_processor_id();
 109
 110        /*
 111         * Select completion CPU
 112         */
 113        if (req->cpu != -1) {
 114                ccpu = req->cpu;
 115                if (!test_bit(QUEUE_FLAG_SAME_FORCE, &q->queue_flags))
 116                        shared = cpus_share_cache(cpu, ccpu);
 117        } else
 118                ccpu = cpu;
 119
 120        /*
 121         * If current CPU and requested CPU share a cache, run the softirq on
 122         * the current CPU. One might concern this is just like
 123         * QUEUE_FLAG_SAME_FORCE, but actually not. blk_complete_request() is
 124         * running in interrupt handler, and currently I/O controller doesn't
 125         * support multiple interrupts, so current CPU is unique actually. This
 126         * avoids IPI sending from current CPU to the first CPU of a group.
 127         */
 128        if (ccpu == cpu || shared) {
 129                struct list_head *list;
 130do_local:
 131                list = this_cpu_ptr(&blk_cpu_done);
 132                list_add_tail(&req->ipi_list, list);
 133
 134                /*
 135                 * if the list only contains our just added request,
 136                 * signal a raise of the softirq. If there are already
 137                 * entries there, someone already raised the irq but it
 138                 * hasn't run yet.
 139                 */
 140                if (list->next == &req->ipi_list)
 141                        raise_softirq_irqoff(BLOCK_SOFTIRQ);
 142        } else if (raise_blk_irq(ccpu, req))
 143                goto do_local;
 144
 145        local_irq_restore(flags);
 146}
 147
 148/**
 149 * blk_complete_request - end I/O on a request
 150 * @req:      the request being processed
 151 *
 152 * Description:
 153 *     Ends all I/O on a request. It does not handle partial completions,
 154 *     unless the driver actually implements this in its completion callback
 155 *     through requeueing. The actual completion happens out-of-order,
 156 *     through a softirq handler. The user must have registered a completion
 157 *     callback through blk_queue_softirq_done().
 158 **/
 159void blk_complete_request(struct request *req)
 160{
 161        if (unlikely(blk_should_fake_timeout(req->q)))
 162                return;
 163        if (!blk_mark_rq_complete(req))
 164                __blk_complete_request(req);
 165}
 166EXPORT_SYMBOL(blk_complete_request);
 167
 168static __init int blk_softirq_init(void)
 169{
 170        int i;
 171
 172        for_each_possible_cpu(i)
 173                INIT_LIST_HEAD(&per_cpu(blk_cpu_done, i));
 174
 175        open_softirq(BLOCK_SOFTIRQ, blk_done_softirq);
 176        cpuhp_setup_state_nocalls(CPUHP_BLOCK_SOFTIRQ_DEAD,
 177                                  "block/softirq:dead", NULL,
 178                                  blk_softirq_cpu_dead);
 179        return 0;
 180}
 181subsys_initcall(blk_softirq_init);
 182